Although there is general agreement that pulmonary capillaries restrict passage of proteins based on their size the selectivity properties of capillaries for differently charged macromolecules are more controversial. Tissue uptake and electron micrograph studies support a negative barrier hypothesis while acute lymph studies indicate a positive capillary barrier. We have proposed an interstitial cation exchange mechanism based on interstitial distribution studies of lactate dehydrogenase (LDH) isozymes which appears to reconcile these two positions. In the proposed research we will specifically characterize pulmonary endothelial permeability in terms of permeability-surface area products (PS) and reflection coefficients (sigma) for two globular proteins LDH 1 (pI=5.0) and LDH 5 (pI=7.9), which have the same molecular weight (140,000 MW) but different net charges at blood pH. Tissue clearances of LDH and in vivo osmotic pressures of negative and neutral dextrans will be used to minimize the effect of interstitial fixed negative charges on transport data. These studies should reveal the magnitude and surface charge of the endothelial layer itself. We will also determine how the interstitial and basement membrane charged groups affect the backward egress of anionic and cationic LDH isozymes from the interstitium across the capillaries and also from interstitium into pulmonary lymph. In addition, we will measure the transport rates of LDH isozymes across the airway epithelium into lymph and plasma. The role of polycation infusion (protamine sulphate, the charge on plasma colloids, and serum permeability factors in charge related permselectivity and overall microvascular protein and water permeability will also be studied. Because chemotaxis and activation of polymorphonuclear leukocytes (PMNs) appears to be charge related, the effects of polycation dose and polyanion intervention on PMN induced microvascular damage will be studied. These data should allow separation of charge permselectivity between solute and pore from interstitial charge effects, direct endothelial damage due to polycations, and PMN induced capillary damage caused by polycations. A second focus is a further characterization of pulmonary interstitial fluid conductance during oleic acid injury and at increased transpulmonary pressures.